The cementation of surgical implants within the intramedullary canal of a patient's bone has proven to be a surgical procedure of great benefit to mankind. The most common example of this procedure is the implantation of a femoral prosthesis within the intramedullary canal of the femur. Polymethylmethacrylate bone cements, e.g. Surgical Simplex P Bone Cement (Howmedica, Inc.; New York, N.Y.), have been used with great success in this procedure. The bone cement is applied in a viscoelastic state into the prepared intramedullary canal with a bone cement extruder, after which the implant is inserted into the canal. The cement, which polymerizes and hardens in the space between the bone and the implant, functions as a luting agent. The quality of the fixation is greatly enhanced by the mechanical interlocking of the cement with the porous trabecular structure of the cancellous bone of the wall of the intramedullary canal and with any pores, dimples, elevations, keys, etc., provided on the surface of the implant.
Fixation of surgical implants with polymethylmethacrylate bone cements within intramedullary canals has been practiced with great success for many years. On rare occasions, however, problems associated with the premature loosening of the implant in use have been observed. One explanation for these loosening problems is an inadequate penetration of the bone cement into the cancellous bone of the intramedullary canal wall. It is known that this penetration can be improved by pressurizing the viscoelastic bone cement within the intramedullary canal so as to work the cement deeply into the cancellous bone of the canal wall before it hardens. Thus, it is well known to utilize an intramedullary plug to prevent passage of cement distally (with reference to the surgeon) of its desired location within the intramedullary canal (see, for example, U.S. Pat. Nos. 4,245,359; 4,276,659 and 4,293,962, and European Pat. No. 6408). Pressurization can be further improved to some extent by finger packing by the surgeon. Compactors have been used to compress and pressurize bone cement applied to an intramedullary canal. However, the use of a compactor requires the addition of a distinct, time-consuming step to the surgical procedure, with the results being operator intensive, i.e. the extent of pressurization achieved depends upon the axial force exerted by the surgeon. Additionally, it is known to equip the nozzle of a bone cement extruder with a non-inflatable restrictor (e.g. the Miller Bone Cement Injector Restrictor Set; Zimmer USA; Warsaw, Ind.) made of a resilient material to block the flow of cement between the nozzle and the bone through the open end of the prepared intramedullary canal. However, the quality of the seal obtained is limited because the fit of such a restrictor against the prepared bone is more in the nature of a line contact at the open end than a surface-to-surface contact and, furthermore, the quality of the seal will be reduced when the restrictor is unable to completely fill any irregularities in the bone against which it fits. Again, the extent of pressurization achieved depends upon the axial force exerted by the surgeon.